Allow multiple to use the same domain name

[guillemcanal]

Allow multiple containers to use the same domain name.

Uses cases:

• 2 containers can use the same domain name but can provide different paths constraints in Traefik
  • container foo is accessible from foo.domain.fr/ (--label 'traefik.frontend.rule=Host: foo.domain.fr')
  • container foo-admin, is accessible from foo.domain.fr/admin (--label 'traefik.frontend.rule=Host: foo.domain.fr; Path: /admin')